Author Topic: Maestro 612p - troubleshooting help?  (Read 2715 times)

Offline astrenio

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Maestro 612p - troubleshooting help?
« on: July 05, 2015, 10:59:57 AM »
Hi all!

First time post to the forum. I just recently picked up a vintage Maestro 612p from a GoodWill store for a song, and looking on working to get it up and running as a project. I don't have a ton of background in messing with amps & circuits, so I just wanted to reach out to see if there are any pointers from the wealth of experience here on what the most common issues might be and where I can get started on troubleshooting this bad boy. The unit powers on (red indicator light comes on, as well as the sound of what I assume is the speaker powering, a soft little pop), but unfortunately no sound comes while playing. I tried replacing the .7 amp fuse on top of the circuit board, but that didn't do the trick unfortunately. Where should I be looking next? Thanks so much in advance for any and all help you can offer!

--Andrew

Offline pianotuner steveo

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Re: Maestro 612p - troubleshooting help?
« Reply #1 on: July 05, 2015, 11:07:36 AM »
Can you post pictures? Im not sure what this instrument is.
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 270 Butterfly Grand
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
2017 Yamaha P255
2020 Kawai CA99
....and a few guitars...

Offline vanceinatlance

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Re: Maestro 612p - troubleshooting help?
« Reply #2 on: July 05, 2015, 11:40:58 AM »
You might start with the headphone jack plugs. Clean the switch contacts with something like deox. If that dosen't do the trick it may be more complicated. I had to rebuild the high voltage portion of my unit to get it playing again.
Be careful as there is a possible shock hazard and it could be hazardous or leathal if you are not comfortable with electronics.
That being said, i will look for my pics and post them if it helps.
Congrats on your find!

Offline vanceinatlance

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Re: Maestro 612p - troubleshooting help?
« Reply #3 on: July 05, 2015, 12:27:18 PM »
Thos is a pic of my 612p Steveo. It's electronics are like a wurlitzer with reeds and electrostatic pickup. It is IMO, much less expressive, but unique in its own way.

Offline vanceinatlance

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Re: Maestro 612p - troubleshooting help?
« Reply #4 on: July 05, 2015, 12:47:18 PM »
These are some pics of the headphone jack contacts and the high voltage section I ended up rebuilding. Solder job is not as clean as the factory, but she sounds nice now.
If you end up working on the amp, the electrolytic caps would be a good thing to replace while your in there. The amp itself most likely needs a good general cleaning off. The amp is placed exactly where all dust and debris come to a rest. Actually, might not be a bad place to start as a cat hair or something could get in there and have shorted something out. Don't forget to disconnect the power if you are in there!

Offline astrenio

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Re: Maestro 612p - troubleshooting help?
« Reply #5 on: July 05, 2015, 10:34:23 PM »
Thanks for all of the tips, Vance! I'll definitely give those contacts a good deox treatment.  I'm concerned about the shock risk you mentioned if I do have to get into the amp. I plan to work completely unplugged whenever I'm anywhere under the hood, so to speak, but is that sufficient to alleviate the risk of electrical injury? Or is there a latent charge left in the amp even when unplugged? Thanks so much for your wisdom, and fingers crossed it's just a cleaning job that will bring this guy back to life.

Thanks again,

Andrew

Offline vanceinatlance

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Re: Maestro 612p - troubleshooting help?
« Reply #6 on: July 06, 2015, 09:30:00 AM »
Andrew,
if you are not sure, it is probably best to have a tech look at it. Capacitors can and do keep a charge when a unit is unplugged and can zap you 8f you are not careful. This circuit doesn't have very large filter capacitors ,so it is not as likely to hurt someone, but you should treat it as if the risk is always there.
You might try blowing off the board "unplugged" with an air compressor to clear up the stuff that settled on the circuit. Let it sit for awhile after blowing it off to let any moisture dry before plugging it back in.
Maybe you can find a local tech that might be willing to help you look at the circuit if the previous steps don't work out.

Offline astrenio

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Re: Maestro 612p - troubleshooting help?
« Reply #7 on: July 10, 2015, 12:33:07 PM »
Thanks again for all of the great information Vance, it's been incredibly helpful.

I cleaned off (with both air and deoxit for connections) pretty much all of the electronics. After doing so, and letting everything dry, I've got a pretty interesting result. The unit still powers on, and when the volume switch is all the way a maximum, there's just the slightest bit of amplification going on. That is to say, I can hear the signal through the speaker, but it's only marginally louder than the tines sounding on their own. It's most noticeable in the bass register, where I can clearly hear the fundamental coming through the speaker (whereas the tines have a bunch of overtones going on).

I'm curious if you have any ideas that might account for this phenomenon? To my mind, it's clear that both the speaker and amp are working, at least to some extent. Just wondering if you might have any other thoughts on the matter, before I go ahead and try to find a tech who could work on this type of instrument around me. Thanks again, and hope you have a great weekend!

Offline vanceinatlance

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Re: Maestro 612p - troubleshooting help?
« Reply #8 on: July 11, 2015, 11:26:00 AM »
Well, without having it in front of me, it's  hard to guess the issue. The other problem we have here is that I probably know just enough to get you into trouble. I am a hobbiest and am not working on these daily.
That being said, it seems like the obvious is that the ampflication is not happening effectively. I would consider any transistor stage where gain is expected,and, it may also be that the voltage at the pickups is not high enough to effectively pick up the vibrration of the reeds (voltage multiplier stage I fixed on mine) and feed the amplification stage.
The schematic is usually posted inside the unit wich makes it much easier for a tech to look at and figure out.
Hope this helps you some.
I would like to hear what the fix ends up being.
Best of luck, and If I can help further, please let me know.
Vance

Offline Max Brink

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Re: Maestro 612p - troubleshooting help?
« Reply #9 on: October 23, 2015, 04:41:45 PM »
Could be as simple as a bad potentiality. Could be a more in depth issue. Did you ever get this solved?

There should be a copy of the schematic inside the unit. Otherwise I should be able to find a copy of it that I took a while back. A qualified amplifier technician or EE should be able to troubleshoot this situation easily. Since there is some output hopefully it is an easy fix!

If anyone out there needs Maestro 612P parts I have an "organ donor" that was pulled from a dumpster behind a music store. Most of the parts are still there and in good condition besides heavy damage to the cosmetic case. It's not worth building a new case for it so if you need parts shoot me an email.
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Offline damonnomad

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Re: Maestro 612p - troubleshooting help?
« Reply #10 on: December 19, 2020, 07:51:55 PM »
These are some pics of the headphone jack contacts and the high voltage section I ended up rebuilding. Solder job is not as clean as the factory, but she sounds nice now.
If you end up working on the amp, the electrolytic caps would be a good thing to replace while your in there. The amp itself most likely needs a good general cleaning off. The amp is placed exactly where all dust and debris come to a rest. Actually, might not be a bad place to start as a cat hair or something could get in there and have shorted something out. Don't forget to disconnect the power if you are in there!

Not sure about the policy on resurrecting ancient threads, but I recently came across and repaired one of these (it just had some simple wiring issues).

It would be great to hear more about your amp and headphone input rebuild. Did you just replace the capacitors part-for-part, or did you make any changes while you were in there?

I can get some nice close-mic sounds out of it, but so far I can't get a usable line-out signal because of what sounds like insane levels of 60-cycle hum and even a bit of radio coming though. Did you ever experience hum issues or was your amp relatively quiet after your recap?

Offline damonnomad

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Re: Maestro 612p - troubleshooting help?
« Reply #11 on: December 23, 2020, 11:20:37 AM »
As an update, my issue ended up being a simple ground loop that was quickly solved by plugging my amp and keyboard into the same outlet.